The present invention relates to a system and method for synchronization within a communication network, in particular between a sender and a receiver. The invention provides transfer of phase information, preferably but not exclusively by transfer of phase, e.g. absolute synchronization input phase, within one or more packets, e.g. multicast packets.
In TDM traffic the synchronization is transferred via the carrier itself (optical systems) or under use of a dedicated timeslot. However this demands for a continuous data transmission.
Synchronizing the carrier to an external clock source requires heavy filtering of the external clock in order not to violate the carrier clock jitter requirements. The exact time when a packet is sent cannot be predicted beforehand, because it is depending on the existing data queues.
Transfer of synchronization information over packet networks may be effected with timestamps which are transmitted every 50 ms+/−3 ms. The information is sent very seldom and the delay jitter is large. Consequently the filter times at the destination point are extremely long (up to several hours). In principle this is not feasible for packet based radio transmission.
U.S. Pat. No. 5,260,978 provides a Residual Time Stamp (RTS) technique for recovering the timing signal of a constant bit rate input service signal at the destination node of a synchronous ATM telecommunication network. At the source node, a free-running P-bit counter counts cycles in a common network clock. The current count of the P-bit counter, defined as the RTS, is transmitted in the ATM adaptation layer. At the destination node, a pulse signal is derived in which the periods are determined by the number of network clock cycles represented by the received RTSs. This pulse signal is then multiplied in frequency by N to recover the source node service clock.